1. Field of the Disclosure
The invention relates generally to a shock absorber, to a logging assembly incorporating the shock absorber, and to methods of using the logging assembly.
2. Related Art
The logging of geological formations is, as is well known, economically a highly important activity. The invention is of benefit in logging activities potentially in all kinds of mining and especially in the logging of reserves of oil and gas, water or other valuable commodities.
Virtually all commodities used by mankind are either farmed on the one hand or are mined or otherwise extracted from the ground on the other, with the extraction of materials from the ground providing by far the greater proportion of the goods used by humans.
It is extremely important for an entity wishing to extract materials from beneath the ground to have as good an understanding as possible of the lithology of a region from which extraction is to take place.
This is desirable partly so that an assessment can be made of the quantity and quality, and hence the value, of the materials in question; and also because it is important to know whether the extraction of such materials is likely to be problematic.
In consequence a wide variety of logging methods has been developed over the years. The logging techniques exploit physical and chemical properties of a formation usually through the use of a logging tool or sonde that is lowered into a borehole (that typically is, but need not be, a wellbore) formed in the formation by drilling.
Typically the sonde sends energy into the formation and detects the energy returned to it that has been altered in some way by the formation. The nature of any such alteration is processed into electrical signals that are then used to generate logs (i.e. numerical, graphical or tabular representations containing much data about the formation in question).
The logging sondes usually are elongate, rigid cylinders that might be 2 m or more in length and between about 57 mm (21/4 inches) and 203 mm (8 inches) in diameter. A toolstring containing a sonde might be considerably longer, with toolstring lengths in the range 5-10 m being known.
A toolstring is normally conveyed from a surface location to a chosen location in a well or borehole, that typically but not necessarily is near its total depth (TD), by being supported on drillpipe that is fed into the well or borehole.
As is well known, drillpipe is elongate, hollow, hardened steel tubing that is provided in the form discrete so-called “stands” or “joints” of standard lengths (typically about 10 m or 30 feet each) that may be screwed one to another by way of so-called “pin” and “box” ends to create long tubes that might be hundreds or thousands of meters long.
Each stand of drillpipe includes at one, in use uphole, end a socket (box) that is threaded and at its in-use downhole end a threaded exterior section (pin) that can be threadedly received in the socket of an adjacent drillpipe stand.
Drillpipe can be used to support various kinds of logging tool or toolstring in order to permit their conveyance into a well or borehole. It is known in this regard to convey logging tools shielded inside the hollow interior of drillpipe while the latter is run in to the location, underground, at which logging is to take place. The logging toolstring may then be caused to move partially to protrude from the drillpipe so that logging may commence. The drillpipe is withdrawn at a chosen speed in an uphole direction (with successive stands being removed at the surface location as their connections to the adjacent drillpipe below become exposed) while logging of the formation takes place.
Data resulting from the logging process are in one way or another transmitted to a computer at a surface location (that may be at the wellhead, or at a location far removed from the oil or gas field under investigation) that through the use of installed software produces logs that typically but not necessarily are in a graphical form. Other software and/or skilled human analysts then can interpret the logs and from them obtain much valuable information about the subterranean conditions in the formation logged.
The internal circular diameter of most drillpipe in use is less than 100 mm (4 inches) yet several sondes or other elements of a logging toolstring extend in at least one transverse dimension over a greater width. As a consequence such elements cannot be conveyed downhole inside drillpipe because they are too large or too wide.
Such tool elements may need to be conveyed downhole in an unprotected manner. This exposes them to extremely harsh conditions caused by e.g. the pressure of fluids in a well, extremes of temperature, aggressive chemicals and impacts with rock or other equipment.
Aside from the fact that logging toolstring elements often are very valuable in themselves any damage to such elements may cause costly delays in oilfield exploration or completion, or may result in leakage of substances the handling of which is subject to strict regulation, or the release of large amounts of energy. For a variety of reasons therefore there is a need to improve the conveyance of (in particular) one or more logging toolstring elements each having a diameter, or at least one transversely extending dimension, that is too large to permit conveyance inside drillpipe.
Even if the logging toolstring does not contain any elements that are too wide to be conveyed inside drillpipe, and the whole toolstring may be accommodated inside drillpipe during running in, a need exists for improvements in the apparatuses and methods used at the time of deployment of logging sondes forming parts of toolstrings.